Polypropylene resin composition and expanded molding

ABSTRACT

A polypropylene-based resin composition is provided that can provide a foam molding that exhibits an excellent closed cell characteristic and excellent extrusion characteristics, that is light weight and has a rigid feel, and that has an excellent recyclability. 
     This polypropylene-based resin composition contains 100 weight % or is less than 100 weight % but at least 70 weight % of component (A) below and contains 0 weight % or is greater than 0 weight % but not more than 30 weight % of component (B) below,
         component (A):
           a propylene-based resin composition that comprises at least the following two components: a propylene-α-olefin copolymer (A1) satisfying conditions (A-1) to (A-3) and a propylene homopolymer (A2), (A1) and (A2) being obtained by polymerization by a multistage polymerization method, and this propylene-based resin composition having a content of (A1) of 1 to 20 weight % and a content of (A2) of 99 to 80 weight %, having a melt flow rate in the range from 5 to 20 g/10 minutes and exhibiting strain hardening in a measurement of extensional viscosity at a temperature of 180° C. and a strain rate of 10 s −1 ,   
               (A-1) an α-olefin content of 15 to 85 weight %,   (A-2) an intrinsic viscosity η of 5 to 20 dL/g,   (A-3) a Mw/Mn of 5 to 15;
       component (B):
           a propylene-based resin composition comprising at least the following two components: a propylene homopolymer or a propylene-α-olefin copolymer having a content of non-propylene α-olefin of less than 1 weight % (B1), which has an MFR of 10 to 1000 g/10 minutes, and a propylene-α-olefin copolymer (B2) that has a weight-average molecular weight of 500,000 to 10,000,000 and a content of non-propylene α-olefin of 1 to 15 weight %, (B1) and (B2) being obtained by polymerization by a multistage polymerization method, and this propylene-based resin composition having a content of (B1) of 50 to 90 weight % and a content of (B2) of 50 to 10 weight %, and satisfying prescribed conditions (B-1) to (B-3).

TECHNICAL FIELD

The present invention relates to a polypropylene-based resin compositionand to a foam molding, and relates to a polypropylene-based resincomposition that can provide a foam molding that exhibits an excellentclosed cell characteristic and excellent extrusion characteristics, thatis light weight and has a rigid feel, and that has an excellentrecyclability, and also relates to a foam molding obtained using thispolypropylene-based resin composition.

BACKGROUND ART

Polyolefin-based resin foams are light weight and exhibit an excellentheat resistance and impact resistance, and as a result are widely usedin applications such as core materials for automotive interior trim,building materials, stationery, food containers, and so forth.

These polyolefin-based resin foams are obtained, for example, by mixingany of various foaming agents under the application of pressure into amolten polyolefin using an extruder and then carrying out extrusion andfoaming under atmospheric pressure from a die attached at the end of theextruder.

However, a problem with conventional foams has been the difficulty ofmaintaining, in the molten resin, the individual bubbles (also referredto below as “cells”) having the produced gas partial pressure, which hasresulted in the rupture of the individual cells and a pronouncedtendency for open cells to be produced.

Various means for raising the melt tension of the resin used and therebyraising the cell retention force have been proposed as methods forobtaining a foam with few open cells (excellent closed cellcharacteristic).

For example, methods have been proposed in which the melt tension israised through the addition of an ultra-high molecular weight component.However, generally when a resin having a high melt tension is used, thecell retention force is in fact raised, but the viscosity also becomestoo high and an expansion ratio that corresponds to the amount offoaming agent addition is not obtained. Moreover, there is a large loadon the extruder, and, in those instances in which the maintenance of ahigh productivity is sought, the load on the extruder is increased andthe extrusion moldability declines and, in addition, the temperature ofthe resin rises due to shear heat generation and cell growth cannot beinhibited through cooling and open cells are produced.

In addition, polypropylene-based resins that are characterized by a highmelt tension are commercially available in the form of, for example,propylene-based resins that have been subjected to electron beamcrosslinking, as in, e.g., Patent Document 1, and propylene-based resinsthat have been crosslinked using, e.g., a peroxide, as in, e.g., PatentDocuments 2, 3, and 4. However, the use of a crosslinking treatment toraise the melt tension has led to a substantial decline in the meltproperties when the edge from foam sheet molding or the excess aftercontainer molding is returned again to foam sheet molding, anddisadvantage in cost, and due to the crosslinking, this has also beenunsatisfactory with regard to extrusion stability and odor.

CITATION LIST Patent Literature

Patent Document 1 Japanese Patent Application Laid-open No. S62-121704

Patent Document 2 Japanese Patent Application Laid-open No. H6-157666

Patent Document 3 WO 99/27007

Patent Document 4 Japanese Patent Application Laid-open No. 2004-339365

SUMMARY OF INVENTION Technical Problem

The present invention was achieved based on these circumstances and hasas an object the introduction of a foam that exhibits an excellentclosed cell characteristic and excellent extrusion characteristics andthat is light weight, has a rigid feel, and has an excellentrecyclability.

Solution to Problem

As a result of focused investigations regarding this object, the presentinventors discovered that a foam that exhibits an excellent closed cellcharacteristic and excellent extrusion characteristics and that is lightweight, has a rigid feel, and has an excellent recyclability can beproduced by using a material comprising a foaming agent and apolypropylene-based resin composition that has a special constitution.The present invention was achieved based on this discovery.

Thus, the present invention provides a polypropylene-based resincomposition and a foam molding described below.

[1] A polypropylene-based resin composition comprising at least twocomponents (A) and (B) below, wherein, based on 100 weight % for the sumof components (A) and (B), the component (A) content is 100 weight % oris less than 100 weight % but at least 70 weight % and the component (B)content is 0 weight % or is greater than 0 weight % but not more than 30weight %,

-   -   component (A):        -   a propylene-based resin composition that comprises at least            the following two components: a propylene-α-olefin copolymer            (component (A1)) satisfying conditions (A-1) to (A-3) below            and a propylene homopolymer (component (A2)), components            (A1) and (A2) being obtained by polymerization by a            multistage polymerization method, and this propylene-based            resin composition having a component (A1) content of 1 to 20            weight % and a component (A2) content of 99 to 80 weight %            (where the sum of components (A1) and (A2) is 100 weight %),            having a melt flow rate in the range from 5 to 20 g/10            minutes and exhibiting strain hardening in a measurement of            extensional viscosity at a temperature of 180° C. and a            strain rate of 10 s⁻¹,

-   (A-1) an α-olefin content of 15 to 85 weight % (where the total    amount of monomer constituting component (A1) is 100 weight %),

-   (A-2) an intrinsic viscosity η of 5 to 20 dL/g,

-   (A-3) a Mw/Mn of 5 to 15;    -   component (B):        -   a propylene-based resin composition comprising at least the            following two components: a propylene homopolymer or a            propylene-α-olefin copolymer having a content of            non-propylene α-olefin of less than 1 weight % (component            (B1)), which has an MFR of 10 to 1000 g/10 minutes, and a            propylene-α-olefin copolymer (component (B2)) that has a            weight-average molecular weight of 500,000 to 10,000,000 and            a content of non-propylene α-olefin of 1 to 15 weight %,            components (B1) and (B2) being obtained by polymerization by            a multistage polymerization method, and this propylene-based            resin composition having a component (B1) content of 50 to            90 weight % and a component (B2) content of 50 to 10 weight            % (where the sum of components (B1) and (B2) is 100 weight            %), and satisfying the following conditions (B-1) to (B-3),

-   (B-1) an MFR of 0.1 to 20 g/10 minutes,

-   (B-2) the relationship between a melt tension (MT) and the MFR    satisfying the following formula    log MT>−0.97×log MFR+1.23,

-   (B-3) a longest relaxation time (id) of at least 100 seconds.

[2] The polypropylene-based resin composition according to [1], whereinthe component (A) content is 100 weight % and the component (B) contentis 0 weight %.

[3] The polypropylene-based resin composition according to [1], whereinthe component (A) content is 97 to 70 weight % and the component (B)content is 3 to 30 weight %.

[4] The polypropylene-based resin composition according to any one of[1] to [3], wherein component (A) has a strain hardening exponent λmax(10) of at least 1.2 in the measurement of extensional viscosity at atemperature of 180° C. and a strain rate of 10 s⁻¹.

[5] A polypropylene-based resin foam molding molded by adding a foamingagent to the polypropylene-based resin composition according to any oneof [1] to [4], and carrying out extrusion foam molding thereof.

[6] The polypropylene-based resin foam molding according to [5], whereinthe polypropylene-based resin foam molding is a foam sheet molded byextrusion from a slit die or circular die.

[7] A polypropylene-based resin foam thermoformed article formed bythermoforming of the foam sheet according to [6].

[8] A polypropylene-based resin foam hollow molding molded by adding afoaming agent to the polypropylene-based resin composition according toany one of [1] to [4], extruding the same to give a parison, andsubsequently performing blow molding within a mold.

Advantageous Effects of Invention

The polypropylene-based resin composition of the present inventionprovides a foam that exhibits an excellent closed cell characteristicand excellent extrusion characteristics and that is light weight, has arigid feel, and has an excellent recyclability, and in particular canprovide a material favorable for foam (multilayer) sheet applications inextrusion foam molding. The obtained polypropylene-type (multilayer)foam sheet can provide, by thermoforming, moldings that exhibit uniformand microfine foam cells. In addition, a uniform and microfine foamhollow molding can also be obtained by adding a foaming agent to thepolypropylene-based resin composition of the present invention;extruding the same to give a parison; and subsequently performing blowmolding within a mold.

Moreover, these moldings, because they exhibit an excellent appearance,thermoformability, impact resistance, lightness, rigidity, heatresistance, insulation behavior, oil resistance, and so forth, arefavorably used for, for example, stationery files, food containers,beverage cups, display cases, auto parts, commercial and industrialcomponents, and trays.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram of the flow in a CFC-IR measurement.

DESCRIPTION OF EMBODIMENTS

The polypropylene-based resin composition of the present inventioncharacteristically comprises at least two components (A) and (B) below,wherein, based on 100 weight % for the sum of components (A) and (B),the component (A) content is 100 weight % or is less than 100 weight %but at least 70 weight % and the component (B) content is 0 weight % oris greater than 0 weight % but not more than 30 weight %.

-   -   Component (A):        -   a propylene-based resin composition that comprises at least            the following two components: a propylene-α-olefin copolymer            (component (A1)) satisfying conditions (A-1) to (A-3) below            and a propylene homopolymer (component (A2)), components            (A1) and (A2) being obtained by polymerization by a            multistage polymerization method, and this propylene-based            resin composition having a component (A1) content of 1 to 20            weight % and a component (A2) content of 99 to 80 weight %            (where the sum of components (A1) and (A2) is 100 weight %),            having a melt flow rate in the range from 5 to 20 g/10            minutes and exhibiting strain hardening in a measurement of            extensional viscosity at a temperature of 180° C. and a            strain rate of 10 s⁻¹,

-   (A-1) an α-olefin content of 15 to 85 weight % (where the total    amount of monomer constituting component (A1) is 100 weight %),

-   (A-2) an intrinsic viscosity η of 5 to 20 dL/g,

-   (A-3) a Mw/Mn of 5 to 15.    -   Component (B):        -   a propylene-based resin composition comprising at least the            following two components: a propylene homopolymer or a            propylene-α-olefin copolymer having a content of            non-propylene α-olefin of less than 1 weight % (component            (B1)), which has an MFR of 10 to 1000 g/10 minutes, and a            propylene-α-olefin copolymer (component (B2)) that has a            weight-average molecular weight of 500,000 to 10,000,000 and            a content of non-propylene α-olefin of 1 to 15 weight %,            both components (B1) and (B2) being obtained by            polymerization by a multistage polymerization method, the            component (B1) content being 50 to weight % and the            component (B2) content being 50 to 10 weight % (where the            sum of components (B1) and (B2) is 100 weight %), and the            following conditions (B-1) to (B-3) being satisfied,

-   (B-1) an MFR of 0.1 to 20 g/10 minutes,

-   (B-2) the relationship between a melt tension (MT) and the MFR    satisfying the following formula    log MT>−0.97×log MFR+1.23,

-   (B-3) a longest relaxation time (id) of at least 100 seconds.

Here, when component (A) is 100 weight % and component (B) is 0 weight%, the propylene-type resin composition (component (A)) then becomes thepolypropylene-type resin composition of the present invention.

A detailed description follows for each of the components constitutingthe polypropylene-type resin composition of the present invention.

[Component (A)]

Component (A) is a propylene-based resin composition that comprises atleast the following two components: a propylene-α-olefin copolymer(component (A1)) satisfying conditions (A-1) to (A-3) below and apropylene homopolymer (component (A2)), and that has a component (A1)content of 1 to 20 weight % and a component (A2) content of 99 to 80weight % where the sum of components (A1) and (A2) is 100 weight %,

components (A1) and (A2) being obtained by polymerization by amultistage polymerization method,

this propylene-based resin composition having a melt flow rate in therange from 5 to 20 g/10 minutes, and

exhibiting strain hardening in a measurement of extensional viscosity ata temperature of 180° C. and a strain rate of 10 s⁻¹.

(A-1) an α-olefin content of 15 to 85 weight % (where the total amountof monomer constituting component (A1) is 100 weight %)

(A-2) an intrinsic viscosity η of 5 to 20 dL/g

(A-3) a Mw/Mn of 5 to 15

The propylene-based resin composition (A) that is a constituent of thepolypropylene-type resin composition of the present invention iscomprised of at least the aforementioned components (A1) and (A2).

The components (A1) and (A2) encompassed by component (A) are describedin detail below.

<Component (A1)>

Component (A1) is a propylene-α-olefin copolymer.

The α-olefin here is preferably an alkene having not more than 12carbons but excluding propylene, and can be exemplified by ethylene,butene, pentene, hexene, heptene, nonene, decene, 1-methylbutene, and1-methylpentene, whereamong ethylene is particularly preferred.

With regard to the α-olefin content, the α-olefin content using 100weight % for the total amount of monomer constituting component (A1) is15 to 85 weight %, wherein the preferred lower limit value can be 16weight %, 17 weight %, 20 weight %, 30 weight %, or 40 weight %. Thepreferred upper limit value can be 75 weight %, 60 weight %, 50 weight%, or 45 weight %. These upper and lower limit values may be freelycombined. Examples of preferred ranges are 16 to 70 weight %, 17 to 50weight %, and 40 to 60 weight %.

Component (A1) is effective for suppressing the growth of the foamcells, i.e., for lowering the percentage of coalesced cells, and canensure the impact resistance of the foam molding, viscositymodification, and ductility during container molding. When the α-olefincontent is below the lower limit, the effects of an increasedcompatibility with component (A2) and a suppression of foam cell growthare diminished. In addition, at above the upper limit, the compatibilitywith component (A2) conversely ends up deteriorating too much and theinterfacial strength between components (A1) and (A2) weakens and theeffect of suppressing foam cell growth is diminished.

The intrinsic viscosity η of component (A1) must be 5 to 20 dL/g and ispreferably 6.5 to 17 dL/g, 8 to 15 dL/g, or 10 to 20 dL/g. This range isset for the intrinsic viscosity η for the following reasons: since thepropylene-α-olefin copolymer inhibits cell growth, a larger molecularweight provides a higher inhibition of tensile deformation of the cellwall, while cell growth is prevented when it is too large.

This intrinsic viscosity is the value measured at a temperature of 135°C. using decalin as the solvent and using a Ubbelohde capillaryviscometer. To determine the intrinsic viscosity of component (A1), asmall amount of component (A2) is withdrawn during the course of thesequential polymerization and its intrinsic viscosity is measured; theintrinsic viscosity of the overall mass of the components is measuredafter the completion of the sequential polymerization; and thedetermination is made using the following formula.intrinsic viscosity of component (A1)=[intrinsic viscosity of theoverall mass of the components−{intrinsic viscosity of component(A2)×weight fraction of component (A2)/100}]/{weight fraction ofcomponent (A1)/100}

The Mw/Mn of the propylene-α-olefin copolymer must be 5 to 15 and ispreferably 10 to 15. The Mw/Mn is an index of the width of the molecularweight distribution, and, since the propylene-α-olefin copolymersuppresses cell growth, a broader molecular weight distribution moreefficiently restrains tensile deformation of the cell wall. Its effectsare impaired at 5 or below, while it is quite difficult to produce at 15or above.

<Component (A2)>

Component (A2) is a propylene homopolymer. The melt flow rate (MFR) forthe propylene homopolymer (component (A2)) at a load of 2.16 kg and 230°C. is preferably 2 to 80 g/10 minutes, more preferably 5 to 40 g/10minutes, and even more preferably 10 to 30 g/10 minutes. When the MFR isin this range, this provides a resin composition that is adapted to highproduction rates by virtue of the stiffness, impact resistance, andmolding temperature of the resin composition.

This MFR is the value measured in accordance with JIS K 7210 at 230° C.under a load of 2.16 kg.

This propylene homopolymer (component (A2)) has a stereoregularitypreferably of at least 96% and more preferably of at least 96.5%. Whenthe stereoregularity satisfies this range, the stiffness and heatdistortion temperature are further improved and deformation of themolded article during molding is inhibited.

This stereoregularity is the value measured by a ¹³C-NMR methodology.

<Composition of Component (A1) and Component (A2)>

The propylene-based resin composition (component (A)) that is aconstituent of the polypropylene-based resin composition of the presentinvention contains 1 to 20 weight %, where the sum of components (A1)and (A2) is 100 weight %, of the propylene-α-olefin copolymer (component(A1)) that satisfies the previously indicated conditions and contains 99to 80 weight %, where the sum of components (A1) and (A2) is 100 weight%, of the propylene homopolymer that is component (A2).

As previously indicated, component (A1) is a component that has theeffect of suppressing foam cell growth, and, in order to maintainexcellent mechanical properties and so forth, it must be 1 to 20 weight% and is preferably 3 to 10 weight %. At less than 1 weight %, theinhibitory effect on foam cell growth is reduced and, while thestiffness of the material is raised, the impact resistance is lowered.At greater than 20 weight %, the stiffness is unsatisfactory and theviscosity of the overall resin is raised and little cell nucleiformation occurs, cell growth is hindered, and the expansion ratio isreduced.

The preferred contents for components (A1) and (A2) are 3 to 10 weight %for component (A1) and 97 to 90 weight % for component (A2).

The composition of component (A1) and component (A2) is produced bypolymerization by a multistage polymerization method. Production bymultistage polymerization can provide a fine dispersion of thepropylene-α-olefin copolymer (component (A1)), thereby enabling theappearance of the various properties and hence being preferred.

The molecular weight of the propylene homopolymer must be adjusted tomaintain the melt flow rate (MFR, measured at 230° C. under a load of2.16 kg) of the propylene-based resin composition (component (A))provided by such a multistage polymerization method at 5 to 20 g/10minutes and preferably 8 to 15 g/10 minutes. The melt flow rate is avalue that affects the moldability and the state of the cells, and, whenit is too low, cell growth is hindered and the expansion ratio declinesand, in addition, there is little cell nuclei formation and microfinecells are not obtained. When it is high, maintenance of the drawdownduring extrusion molding is hindered and molding becomes problematic.Components (A1) and (A2) themselves may be provided by individualsingle-stage polymerization methods or by a multistage polymerizationmethod.

In order to obtain a microfine closed cell configuration whilemaintaining an excellent cell growth, the propylene-based resincomposition (component (A)) that is a constituent of thepolypropylene-based resin composition of the present invention exhibitsstrain hardening in a measurement of extensional viscosity at atemperature of 180° C. and a strain rate of 10 s⁻¹ In particular, thestrain hardening exponent λmax (10) measured at a temperature of 180° C.and a strain rate of 10 s⁻¹ is preferably at least 1.2 and morepreferably is at least 1.8. While there is no rule for the upper limiton λmax (10), it is generally not more than approximately 10.

The method for measuring the strain hardening exponent λmax (10) of thepropylene-based resin composition and the polypropylene-based resincomposition in the present invention will now be described.

The extensional viscosity at a temperature of 180° C. and a strainrate=10 s⁻¹ is plotted on a log-log graph using the time t (s) on thehorizontal axis and the extensional viscosity η_(E) (Pa·s) on thevertical axis. The viscosity immediately before the occurrence of strainhardening approximates a straight line on this log-log graph. A commonlyused press molder is used for sample production. The temperature of thepress molder is set to 190° C. and preheating is first performed for 90seconds in a state in which pressure is not applied. This is followed byholding for 30 seconds at a pressure of about 30 kg/cm² for degassingand finally molding by the application of pressure at 100 kg/cm² for 60seconds.

The method for analyzing the obtained data will now be considered.Specifically, the slopes at the individual times are first determinedwhen the extensional viscosity is plotted versus time, and variousaveraging methods may be applied thereto considering that themeasurement data for the extensional viscosity is discrete. For example,in one method the slopes for the neighboring data are each determinedand a moving average is taken with the surrounding points. In the regionof low amounts of strain, the extensional viscosity takes the form of amonotonically increasing relationship and gradually asymptoticallyapproaches a constant value. In the absence of strain hardening, itagrees with the Trouton viscosity after the elapse of a sufficientamount of time. However, when strain hardening is present, theextensional viscosity generally begins to increase with time from astrain amount (=strain rate×time) of about 1. That is, theaforementioned slope presents a diminishing tendency with time in thelow strain region, but conversely assumes an increasing tendency from astrain amount of about 1, and an inflection point is present on thecurve in the plot of extensional viscosity versus time. When thisincrease is in fact observed, the assessment is made that strainhardening occurs. Thus, in the strain amount range from about 0.1 to2.5, the point is determined at which the slopes for the individualtimes determined as indicated above assume a minimum value; a tangentline is drawn at this point; and the straight line is extrapolated to astrain amount of 4.0. The maximum value (ηmax) of the extensionalviscosity η_(E) up to a strain amount of 4.0 is determined, while theviscosity on the above-referenced approximate straight line up to thistime is taken to be ηlin. ηmax/ηlin is defined as λmax (10).

The methods for measuring the intrinsic viscosity, molecular weightdistribution, and α-olefin content in the propylene-α-olefin copolymerare considered in the following.

1. Analytical Instrumentation Used

-   -   The cross fractionation instrument        -   CFC T-100 (abbreviated as “CFC” below) from DIA Instruments            Co., Ltd.    -   Fourier-transform infrared absorption spectral analysis FT-IR,        from PerkinElmer Co., Ltd., 1760X

The fixed-wavelength infrared spectrophotometer attached as the detectorfor the CFC is removed and the FT-IR is connected in its place and thisFT-IR is used as the detector. The transfer line between the FT-IR andthe outlet for the solution eluted from the CFC has a length of 1 m, andthe temperature is held at 140° C. throughout the measurement period.The flow cell installed at the FT-IR has an optical path length of 1 mmand an optical path width of 5 mmp, and the temperature is held at 140°C. throughout the measurement period.

-   -   Gel permeation chromatography (abbreviated as “GPC” below)

Three “AD806MS” (product name, Showa Denko Kabushiki Kaisha) columnsconnected in series are used as the GPC column in the CFC second stage.

2. CFC Measurement Conditions

-   -   solvent: ortho-dichlorobenzene (ODCB)    -   sample concentration: 4 mg/mL    -   injection amount: 0.4 mL    -   crystallization: temperature dropped from 140° C. to 40° C. over        approximately 40 minutes    -   fractionation method:

The fractionation temperatures during temperature-rising elutionfractionation are 40, 100, and 140° C., and fractionation into a totalof 3 fractions is carried out. The elution percentages (unit: weight %)for the component eluting at less than or equal to 40° C. (fraction 1),the component eluting at 40 to 100° C. (fraction 2), and the componenteluting at 100 to 140° C. (fraction 3) are respectively defined as“W40”, “W100”, and “W140”. W40+W100+W140=100. Each of the fractionatedfractions is directly and automatically transported to the FT-IRanalytical instrument.

-   -   solvent flow rate during elution: 1 mL/minute

3. FT-IR Measurement Conditions

After elution of the sample solution from the GPC of the CFC secondstage has begun, FT-IR measurement using the conditions indicated belowis performed and the GPC-IR data for each of the above-describedfractions 1 to 3 is acquired.

A schematic diagram of the CFC-FT-IR system structure is given in FIG.1.

detector: MCT

resolution: 8 cm⁻¹

measurement interval: 0.2 min (12 seconds)

number of scans per measurement: 15

4. Postprocessing and Analysis of the Measurement Results

The elution amount and molecular weight distribution for the componentseluted at each temperature are determined using the absorbance at 2945cm⁻¹ obtained by FT-IR for the chromatogram. The elution amounts arenormalized by having the total of the elution amounts for the individualeluted components be 100%. The conversion from retention volume tomolecular weight is performed using a preliminarily constructedcalibration curve obtained using standard polystyrene. The specificmethodology is the same as described above.

The ethylene content distribution of each eluted component (thedistribution of the ethylene content along the molecular weight axis) isdetermined using the ratio between the absorbance at 2956 cm⁻¹ and theabsorbance at 2927 cm⁻¹ obtained by the GPC-IR and converting to theethylene content (weight %) using a calibration curve constructed inadvance using polyethylene, polypropylene, ethylene-propylene rubber(EPR) having a known ethylene content provided by, for example, ¹³C-NMRmeasurement, and their mixtures.

<Content of the Propylene-α-Olefin Copolymer>

Using a propylene-ethylene copolymer (referred to below as “EP”), inwhich the α-olefin is ethylene, as the example for the purposes of theexplanation, the content of the propylene-α-olefin copolymer (component(A1)) in the polypropylene-based resin composition in the presentinvention is defined by the following formula (I) and is determined bythe procedure described below.EP content (weight %)=W40×A40/B40+W100×A100/B100+W140×A140/B140   (I)

In formula (I), W40, W100, and W140 are the elution percentages (unit:weight %) for the individual fractions that have been described above;A40, A100, and A140 are the average ethylene contents (unit: weight %)actually measured for each of the fractions corresponding to W40, W100,and W140; and B40, B100, and B140 are the ethylene contents (unit:weight %) of the propylene-ethylene copolymers present in each fraction.The procedures for determining A40, A100, A140, B40, B100, and B140 aredescribed below.

The meaning of formula (I) is as follows.

The first term on the right-hand side of formula (I) is a term thatcalculates the amount of EP contained in fraction 1 (portion soluble at40° C.). When fraction 1 contains only EP and does not contain apropylene homopolymer (referred to below as “PP”), W40 contributes tothe EP content of fraction 1 origin what it accounts for in the whole assuch; however, the presence in fraction 1, in addition to theEP-originating component, of a small amount of a PP-originatingcomponent (component having a very small molecular weight and atacticpolypropylene) requires correction for this portion. Thus, the EPcomponent-originating amount in fraction 1 is calculated by multiplyingW40 by A40/B40. For example, when the average ethylene content (A40) infraction 1 is 30 weight % and the ethylene content (B40) of the EPpresent in fraction 1 is 40 weight %, 30/40=¾ (i.e., 75 weight %) forfraction 1 originates from EP and the remaining ¼ originates from PP.This step of multiplying by A40/B40 in the first term on the right-handside represents the calculation of the EP contribution from the weight %of fraction 1 (W40). This is also the same for the second and followingterms on the right-hand side, and the EP content is obtained bycalculating the EP from each individual fraction and summing these.

(1) As indicated above, the average ethylene content for the fractions 1to 3 obtained by the CFC measurement is labeled, respectively, A40,A100, and A140 (the unit is weight % for all of these). The procedurefor determining the average ethylene content is described below.

(2) The ethylene content corresponding to the peak location in thedifferential molecular weight distribution curve of fraction 1 isindicated by B40 (unit: weight %). With regard to fractions 2 and 3, itis thought that the rubber portion elutes completely at 40° C. anddesignation by the same definition is not possible, and B100 =B140 =100is therefore defined for the present invention. B40, B100, and B140 arethe ethylene contents of the EP present in the individual fractions, butan analytical determination of these values is substantially impossible.The reason for this is that no means exists for completely separatingfractionating the PP and EP commingled in a fraction. As a result ofinvestigations using various model samples, it was found that theimprovements in the material properties could be well accounted for byhaving B40 be the ethylene content corresponding to the peak location inthe differential molecular weight distribution curve for fraction 1. Inaddition, for the following 2 reasons, approximating both B100 and B140with 100 approximates the actual situation and produces almost no errorin the calculations: the presence of the crystallinity originating withthe ethylene chain, and the amount of EP present in these fractions isrelatively small in comparison to the amount of EP present infraction 1. The analysis is therefore carried out using B100=B140=100.

(3) The EP content is determined according to the following formula(II).EP content (weight %)=W40×A40/B40+W100×A100/100+W140×A140/100   (II)

W40×A40/B40, which is the first term on the right-hand side of formula(II), represents the crystallinity-free EP content (weight %), whileW100×A100/100+W140×A140/100, which is the sum of the second and thirdterms, represents the crystallinity-containing EP content (weight %).

This A40, A100, and A140—which are the average ethylene contents of theindividual fractions 1 to 3 yielded by the CFC measurement—and B40 aredetermined as follows.

The following are determined for the fraction 1 fractionated based ondifferences in the crystal distribution: a curve provided by measuring_(t)he molecular weight distribution with the GPC column that is a partof the CFC analytical instrument, and an ethylene content distributioncurve measured in correspondence to the molecular weight distributioncurve, by the FT-IR connected after the GPC column. The ethylene contentcorresponding to the peak position in the differential molecular weightdistribution curve is taken to be B40.

In addition, the overall sum of the products of the weight % at eachindividual data point and the ethylene content for each individual datapoint, which are acquired as data points during the measurement, istaken to be the average ethylene content A40.

The significance of the three fractionation temperatures is as follows.The significance of the 40° C. in this CFC analysis is that this is thenecessary and sufficient temperature condition for the fractionation ofonly crystallinity-free polymer (for example, the majority of the EP,or, within the PP, the component having a very low molecular weight andthe atactic component). The significance of the 100° C. is that this isthe necessary and sufficient temperature for eluting only the componentthat is insoluble at 40° C. but soluble at 100° C. (for example, thelow-crystallinity PP and, within the EP, the component havingcrystallinity that originates in ethylene and/or propylene chains). Thesignificance of the 140° C. is that this is the necessary and sufficienttemperature for eluting only the component that is insoluble at 100° C.but soluble at 140° C. (for example, within the PP, the component thathas a particularly high crystallinity, and, within the EP, the componentthat has a very high molecular weight and ethylene crystallinity) andfor recovering the entire amount of the propylene-based block copolymerused in the analysis. The EP component in W140 is very small and cansubstantially be neglected.ethylene content in the EP (weight%)=(W40×A40+W100×A100+W140×A140)/[EP]  (III)

This [EP] is the previously determined EP content (weight %).

Within the EP, the ethylene content (E) (weight %) of thecrystallinity-free portion is approximated by the value of B40 becausethe elution of the rubber portion is almost entirely complete at lessthan or equal to 40° C.

However, in an analytical method that combines the cross fractionationtechnique described above with FT-IR, an accurate analysis becomesproblematic in those instances in which the ethylene content incomponent (A1) is less than 15 weight % and a large difference incrystallinity with component (A2) is not present and a temperature-basedfractionation cannot then be satisfactorily carried out. In such a case,preferably component (A1) is withdrawn during the course of thesequential polymerization and its molecular weight is measured (thecomonomer content is also measured when a comonomer is copolymerized);the quantitative ratio between component (A1) and component (A2) isdetermined, for example, by a material balance-based calculation or adirect weighing of the weights during the course of the sequentialpolymerization; and the comonomer content of component (A1) is alsodetermined by measuring the α-olefin content of the overall component(A) upon completion of the sequential polymerization and using thefollowing simple addition rule for the weights. The ethylene content of(A1) can be determined using the following formula when ethylene is usedas the comonomer.ethylene content of component (A1)=[ethylene content of the totalmass−{ethylene content of component (A1)×weight fraction of component(A1)/100}]/{weight fraction of component (A2)/100}

With regard to the quantitative ratio between component (A1) andcomponent (A2), this can also be determined—when a production is carriedout that provides a certain difference between the average molecularweights of components (A1) and (A2)—by carrying out a GPC measurement onthe total mass after the completion of the sequential polymerization;running a peak separation on the obtained multimodal molecular weightdistribution curve using, for example, a commercially available dataanalysis software; and calculating their weight ratio.

After the amount of component (A2) has been determined proceeding asdescribed, the intrinsic viscosity of component (A2) can be determinedusing the following formula from the amount of component (A2), theintrinsic viscosity of component (A1) provided by sampling andassessment during the course of polymerization, and the intrinsicviscosity of the total mass (Y).intrinsic viscosity of component (A1)=[intrinsic viscosity of the totalmass (Y)−{intrinsic viscosity of component (A2)×weight fraction ofcomponent (A2)/100}]/{weight fraction of component (A1)/100}

<Production Method >

The production of the propylene-based resin composition that iscomponent (A) is carried out using a multistage polymerization method,but there are no particular limitations thereon as long as thehereinabove described properties are present, and an appropriateselection may be made from known multistage polymerization methods andconditions.

A highly stereoregular catalyst is ordinarily used as the propylenepolymerization catalyst. For example, Ziegler catalysts are preferred,such as catalysts that combine an organoaluminum compound and anaromatic carboxylic acid ester with a titanium trichloride compositionobtained by reducing titanium tetrachloride with an organoaluminumcompound followed by treatment with various electron donors and electronacceptors (refer to Japanese Patent Application Laid-open Nos.S56-100806, S56-120712, and S58-104907) and supported catalysts providedby contacting a magnesium halide with titanium tetrachloride and variouselectron donors (refer to Japanese Patent Application Laid-open Nos.S57-63310, S63-43915, and S63-83116).

The propylene-based resin composition is obtained by the polymerizationof propylene followed by the random polymerization of propylene and anα-olefin, particularly preferably ethylene, in the presence of apolymerization catalyst using a production process such as, for example,a gas-phase polymerization method, liquid-phase bulk polymerizationmethod, or slurry polymerization method. Multistage polymerization by aslurry method or a gas-phase fluidized bed method is preferred forobtaining a propylene-based resin composition (component (A)) that hasthe various properties described in the preceding.

The polymerization to give the propylene homopolymer (component (A2))may be a single-stage polymerization or multistage polymerization ofpropylene.

The multistage polymerization to give the propylene homopolymer can beexemplified by the following two-stage polymerization method having astep (1) and a step (2).

Step (1):

The propylene is polymerized in the presence of hydrogen as a molecularweight regulator in order to suppress the production of polymer with anexcessively large molecular weight. Hydrogen is added so as to providean MFR for the propylene polymer portion of preferably at least 150 g/10minutes. The hydrogen concentration is generally selected from the rangeof 0.1 to 40 mol % with reference to the total amount of monomer. Thepolymerization temperature is generally selected from 40 to 90° C. andthe pressure is generally selected from 0.1 to 5 MPa. The amount ofpolymer obtained in this step (1) is preferably adjusted to providegenerally from 80 to 99 weight % of the total amount of polymerization.When the amount of the propylene polymer produced in this step (1) isless than 80 weight %, the high molecular weight propylene polymerproduced in step (2) becomes too prominent and the moldability is thenreadily impaired.

Step (2):

In order to carry out polymerization into a propylene polymer having ahigher molecular weight than the propylene polymer produced in step (1),the polymerization in step (2) is carried out in an atmosphere that hasa hydrogen concentration that is as low as possible or is carried outunder conditions in which hydrogen is substantially not present. Thepolymerization is run successively in the presence of the propylenepolymer produced in step (1) and a catalyst. The polymerizationtemperature is generally selected from the range of 40 to 90° C. and thepressure is generally selected from the range of 0.1 to 5 MPa. Theamount of polymer obtained in this step (2) is generally preferablyadjusted to provide 1 to 20 weight % of the total amount ofpolymerization. Any combination may be used as long as the propertyvalues of the overall polymer yielded by the combination of step (1) andstep (2) can be brought into the previously described ranges.

The polymerization to give the propylene homopolymer (component (A2))portion is followed by polymerization to give the propylene-α-olefincopolymer (component (A1)) portion. The propylene-α-olefin copolymerportion must be executed as a high molecular weight propylene-α-olefincopolymer in order to bring the intrinsic viscosity and molecular weightdistribution (Mw/Mn) to the prescribed values.

In order to carry out polymerization into a high molecular weightpolymer, the polymerization to give the propylene-α-olefin copolymerportion preferably is carried out in an atmosphere that has a hydrogenconcentration that is as low as possible or is carried out underconditions in which hydrogen is substantially not present. Thepolymerization is run successively and in the presence of a catalyst andthe propylene homopolymer produced in the polymerization step for thepropylene homopolymer. The polymerization temperature is generallyselected from the range of 40 to 90° C. and the pressure is generallyselected from the range of 0.1 to 5 MPa.

[Component (B)]

Component (B) is a propylene-based resin composition that is constitutedof components (B1) and (B2) that satisfy the following and are obtainedby a multistage polymerization method.

Component (B1):

A propylene homopolymer or a propylene-α-olefin copolymer having anon-propylene α-olefin content of less than 1 weight %, which has an MFRof 10 to 1,000 g/10 minutes.

Component (B2):

A propylene-α-olefin copolymer having a weight-average molecular weightof 500,000 to 10,000,000 and a non-propylene α-olefin content of 1 to 15weight %.

In addition, component (B) is a propylene-based resin composition thathas a component (B1) content of 50 to 90 weight % and a component (B2)content of 50 to 10 weight % (where the sum of components (B1) and (B2)is 100 weight %) and that satisfies the following conditions (B-1) to(B-3).

-   (B-1) an MFR of 0.1 to 20 g/10 minutes-   (B-2) the relationship between the melt tension (MT) and the MFR    satisfying the following formula    log MT>−0.97×log MFR+1.23-   (B-3) a longest relaxation time (τd) of at least 100 seconds

A catalytic system composed mainly of a titanium-containing solidcatalyst component and an organoaluminum compound, or a metallocenetransition metal compound that has at least one conjugated π-electronligand, can be used as the catalytic system for obtaining thepropylene-based resin composition having the indicated properties(component (B)).

The metallocene compound may also be used with an aluminoxane as acocatalyst and may be used supported on silica or a clay mineral.Preferred specific examples of metallocene catalysts are the catalystsdescribed in Japanese Patent Application Laid-open Nos. H8-217928,H8-238731, H8-183814, H8-208733, H8-85707 and the like.

The titanium-containing solid catalyst component is selected from knownsupported catalyst components obtained by contacting a solid magnesiumcompound, a titanium tetrahalide, and an electron donor compound andfrom known catalyst components that contain titanium trichloride astheir main component.

The aluminum compound for the cocatalyst is represented by the generalformula AlR_(n)X_(3-n) (in the formula, R represents a C₂₋₁₀ hydrocarbylgroup, X represents a halogen atom such as chlorine, and n represents anumber defined by 3≧n>1.5).

When the titanium-containing solid catalyst component is asupport-supported catalyst component that contains a solid magnesiumcompound, the use of AlR₃ or a mixture of AlR₃ and AlR₂X is preferred.When, on the other hand, it is a catalyst component that containstitanium trichloride or contains titanium trichloride as its maincomponent, the use of AlR₂X is preferred.

Known electron donor compounds can be used as the third component inaddition to these catalysts and cocatalyst components.

The polymerization reaction to obtain the propylene-based resincomposition (component (B)) can be run, for example, in the presence ofan inert solvent, e.g., hexane or heptane, or in the absence thereof,i.e., in the presence of liquid propylene or in gas-phase propylene. Thereaction can be run in batch mode using one polymerization kettle or canbe run continuously by connecting two or more polymerization kettles inseries. With regard to the polymerization sequence, a two-stageexecution is preferred in which the polymerization to give component(B1) is carried out initially followed by the polymerization to givecomponent (B2). Additional polymerizations in three stages or fourstages may also be carried out.

The catalyst is generally added prior to the polymerization in the firststage. Replenishment of the catalyst in an ensuing stage is notnecessarily ruled out, but the addition of catalyst in the first stageis preferred in order to obtain properties not obtained with a resinblend.

The additional α-olefin that is copolymerized with propylene can bespecifically exemplified by ethylene, 1-butene, 1-hexene, 1-octene, andso forth, wherein ethylene is particularly preferred.

A two-stage method in which polymerization to give component (B1) isperformed initially followed by polymerization to give component (B2) isdescribed in detail in the following.

In a step (1) for obtaining component (B1), the polymerization ofpropylene or propylene and a small amount of another olefin is carriedout in the presence of hydrogen. The hydrogen preferably controls theMFR of the polymer yielded by step (1) into the range from 10 to 1000g/10 minutes. At an MFR of 10 or below, the viscosity of the total massends up being reduced and microfine cells are then not obtained; atabove 1000, the cell growth inhibiting effect is diminished and anundesirable open cell state occurs. The hydrogen concentration (denotesthe gas-phase concentration in a slurry polymerization, the content inthe monomer in polymerization in liquid propylene, and the content inthe monomer in a gas-phase method) is generally an addition at 1 to 50mol % and preferably 3 to 30 mol %. The other olefin that iscopolymerized with the propylene may be added intermittently or may besupplied continuously, for example, with the propylene. Thepolymerization temperature in step (1) is generally 40 to 90° C., andfrom 50 to 90 weight % and preferably 60 to 80 weight % of the overallamount of polymerization is produced.

The step (2) for obtaining component (B2) is a polymerization in orderto obtain a high molecular weight component, and this polymerization isrun in a substantially hydrogen-free state in which the hydrogenconcentration is not more than 0.1 mol %. The weight-average molecularweight of the polymer obtained in step (2) is 500,000 to 10,000,000 andpreferably 800,000 to 5,000,000. At a weight-average molecular weight of500,000 or below, the effect of raising the melt tension is diminished,the inhibitory effect on cell growth is diminished, and an open cellstate occurs, and hence this is undesirable. When, on the other hand,10,000,000 is exceeded, the viscosity of the total mass ends updeclining and microfine cells are not obtained. The polymerizationtemperature is generally 40 to 90° C. and is preferably 50 to 80° C.,while the α-olefin used as the copolymerized comonomer is specificallyselected from, for example, ethylene, 1-butene, 1-hexene, and 1-octene,wherein ethylene is particularly preferred. The content of the α-olefinis 1 to 15 weight % and preferably 3 to 10 weight %. When the comonomercontent is too high or too low, the dispersion of the high molecularweight component deteriorates and the effect of improving the melttension declines.

The polymer obtained in step (2) is 10 to 50 weight % and preferably 20to 40 weight % of the total polymer that is polymerized to givecomponent B. At less than 10 weight %, the effect of boosting the melttension is diminished and the effect of suppressing cell growth isdiminished and an open cell state appears, and hence this isundesirable. At above 50 weight %, the viscosity of the total mass endsup declining and microfine cells are not obtained.

For the weight-average molecular weight, the polymer obtained after thecompletion of the front-stage polymerization and the final polymer areboth measured using GPC, and the weight-average molecular weight can becalculated from the difference between the two and the relationshipbetween the amount of the polymer from the front-stage polymerizationand the amount of the final polymer. The MFR of the final polymeryielded by step (1) and step (2) is preferably 0.1 to 20 g/10 minutesand is more preferably 0.5 to 10 g/10 minutes.

The details for this derivation of the weight-average molecular weightusing GPC are described in the following. The following method was usedfor this example. instrument model used: 150 C from the WatersCorporation measurement temperature: 140° C.

-   solvent: orthodichlorobenzene (ODCB)-   column: 2×Shodex 80M/S from Showa Denko Kabushiki Kaisha-   flow rate: 1.0 mL/minute-   injection amount: 0.2 mL-   sample preparation: For the sample, a 1 mg/mL solution is prepared    using ODCB (containing 0.5 mg/mL 2,6-di-t-butyl-4-methylphenol    (BHT)), with dissolution requiring approximately 1 hour at 140° C.-   molecular weight determination: standard polystyrene method

The conversion from retention volume to molecular weight is carried outusing a calibration curve that has been constructed in advance usingstandard polystyrene. The following commercial products, all from TosohCorporation, are used for the standard polystyrene.

-   -   F380, F288, F128, F80, F40, F20, F10, F4, F1, A5000, A2500,        A1000

The calibration curve is constructed by injecting 0.2 mL of each of thesolutions prepared by dissolution in ODCB (containing 0.5 mg/mL BHT) togive 0.5 mg/mL. A cubic expression obtained by approximation by theleast squares method is used for the calibration curve.

The following numerical values are used for the viscosity expression[η]=K×M^(α) used for the conversion to molecular weight.

PS: K=1.38×10⁻⁴, α=0.7

PE: K=3.92×10⁻⁴, α=0.733

PP: K=1.03×10⁻⁴, α=0.78

-   detector: MIRAN 1A IR detector (measurement wavelength: 3.42 μm)    from FOXBORO.-   column: AD806M/S (3 columns) from Showa Denko Kabushiki Kaisha

The following relationship between the melt tension (MT) and the MFRalso characteristically obtains for the propylene-based resincomposition (component (B)).log MT>−0.97×log MFR+1.23

This relationship represents the balance between the melt tension andthe fluidity. When this formula is satisfied, this corresponds to thepresence of an excellent fluidity and excellent extrusioncharacteristics while at the same time a high melt tension is generated.That is, the propylene-based resin composition (component (B)) thenpresents an excellent balance between the extrusion characteristics andthe processing characteristics, e.g., in blow molding, foam molding,thermoforming, and so forth.

On the other hand, conventional general-purpose polypropylene-basedresin compositions exhibit left-hand side<right-hand side in thepreceding formula, and the fluidity is then worsened because the MFR issmaller at the same MT when compared to the propylene-based resincomposition (component (B)).

Here, the method for measuring the melt tension MT in this example useda Capilograph from Toyo Seiki Seisaku-sho Ltd., and the measurement wasperformed under conditions of a cylinder temperature of 190° C., anorifice L/D=8.1/2.095 (mm), a piston speed of 10 mm/min, and a take-offspeed of 3.9 m/min.

The production of a propylene-based resin composition (component (B))that satisfies the preceding relationship can be achieved by thepreviously described polymerization method, and production can beparticularly preferably carried out by bringing component (B2) to 50 to10 weight % and preferably 40 to 20 weight % and by bringing theweight-average molecular weight of component (B1) to 500,000 to10,000,000 and preferably approximately 500,000 to 5,000,000.

Another characteristic feature of the propylene-based resin composition(component (B)) is that its longest relaxation time (τd) is at least 100seconds. This τd is determined by stress relaxation measurements anddenotes the time until return to a random state prior to deformation viaan orientational relaxation in which molecular chains that have beensubjected to deformation relax without a change in orientation. This idis considered to be closely connected to the processing characteristicsin, e.g., blow molding, foam molding, thermoforming, and so forth, and alarger τd is believed to correlate with better processingcharacteristics. τd is seen to undergo extension due to either a highmolecular weight component or a branched component or due to thepresence of both, but does not necessarily agree with the nonlinearityof the extensional viscosity. That is, τd does not govern thenonlinearity of the extensional viscosity, but does govern the uniformductility during extensional deformation. According to the results ofinvestigations by the present inventors, the processing characteristicsare hindered when τd is less than 100 seconds due to the smallcontribution from long-relaxation-time components. That is, satisfyingτd≧100 seconds is an essential condition for molding processes where ahigh melt tension is required.

For this longest relaxation time (τd), in this example a master curve isconstructed by measuring the relaxation modulus G(t) using an RMS-800Mechanical Spectrometer from Rheometrics, Inc., and using parallelplates with a diameter of 25 mm and a gap of 1.5 mm at temperatures of200° C. and 240° C. and strains of 50 and 100%. Using the obtained G(t),τd was calculated according to the method described in Journal ofPolymer Science, Volume XL, pp. 443-456 (1959).

The production of a propylene-based resin composition (component (B))that has a longest relaxation time (id) of at least 100 seconds can becarried out by the previously described polymerization method, andproduction can be particularly preferably carried out by bringingcomponent (B2) to 50 to 10 weight % and preferably 40 to 20 weight % andby bringing the weight-average molecular weight of component (B1) to500,000 to 10,000,000 and preferably approximately 500,000 to 5,000,000.

[The Polypropylene-Based Resin Composition Comprising Components (A) and(B)]

The components (A) and (B) obtained as described above form apolypropylene-based resin composition well adapted for foaming, byformulation at a quantitative ratio, based on 100 weight % for the sumof components (A) and (B), wherein component (A) is 100 weight % or isless than 100 weight % but at least 70 weight % and component (B) is 0weight % or is greater than 0 weight % but not more than 30 weight %.Component (A) is the component critical for microfine-sizing of thecells, maintaining the appearance of the extrusion foam article, andsecuring the fluidity, impact resistance, and stiffness of thecomposition as a whole, while component (B) is critical as the componentthat imparts the melt tension required for cell inhibition and thatbrings about additional improvements in the drawdown duringthermoforming and blow molding. At not more than 70% component (A), afoam article with an excellent appearance is not obtained and the cellsbecome coarse and the impact resistance also deteriorates.

For the case in which component (B) is an essential component, the rangein which the effects of component (B) are satisfactorily manifested ispreferably 97 to 70 weight % component (A) and 3 to 30 weight %component (B), while a more preferred quantitative ratio is 96 to 70weight % component (A) and 4 to 30 weight % component (B) and morepreferably 95 to 80 weight % component (A) and 5 to 20 weight %component (B).

<Additives>

The polypropylene-based resin composition of the present invention mayas necessary incorporate the auxiliary additive components ordinarilyused in polyolefin, for example, antioxidants, neutralizing agents, heatstabilizers, light stabilizers, ultraviolet absorbers, anti-foggingagents, agents that increase crystallization nuclei, slip agents,antiblocking agents, antiseptics, colorants, flame retardants, and soforth.

A filler may also be added. With regard to its type, it may be aninorganic filler or an organic filler. The inorganic fillers can beexemplified by talc, calcium carbonate, silica, diatomaceous earth,alumina, titanium oxide, magnesium oxide, aluminum hydroxide, magnesiumhydroxide, calcium silicate, glass beads, bentonite, glass flake, glassfiber, carbon fiber, aluminum powder, molybdenum sulfide, boron fiber,potassium titanate, calcium titanate, hydrotalcite, pumice powder, mica,calcium phosphate, and aluminum phosphate, while the organic fillers canbe exemplified by PMMA beads, cellulosic fiber, polyamide fiber, aramidfiber, polyester fiber, rice husks, wood powder, tofu lees, tapiocapowder, rice flour, kenaf fiber, starch powder, and paper powder.

In addition, the following may also be incorporated within a range thatdoes not impair the effects of the present invention: a diluent or thepulverizate of a skeleton or the edge loss produced when a foam moldingis obtained from the polypropylene-based resin composition of thepresent invention, e.g., homopolypropylene, random copolymers ofpropylene with ethylene or α-olefin having 4 or more carbons, and blockcopolymers of propylene with ethylene or α-olefin having 4 or morecarbons, and/or, for the purposes of modification as necessary, anelastomer such as ethylene-propylene rubber, ethylene-propylene-dienerubber, high-density polyethylene, low-density polyethylene, linearlow-density polyethylene, a styrenic elastomer, and so forth, apetroleum resin or cycloolefin resin, a polyethylene wax or petroleumwax, or a different resin, e.g., an ethylene-vinyl acetate copolymer,maleic acid-modified polypropylene, ethylene-vinyl alcohol copolymer,polyethylene terephthalate, polystyrene, ABS resin, and so forth.

The index for their addition is preferably such that the amount ofaddition is controlled that a total content of the component (A1)propylene-α-olefin copolymer is maintained in the range of 1 to 20weight %.

In order to obtain a polypropylene-based resin foam molding using thepolypropylene-based resin composition of the present invention, the useis preferred of a method in which a foaming agent is added to andmelt-mixed into this resin material in an extruder.

For example, an inorganic foaming agent, a volatile foaming agent, or adecomposable foaming agent can be used as the foaming agent, and thesecan also be used in the form of a mixture. The inorganic foaming agentcan be exemplified by carbon dioxide, air, nitrogen, and so forth. Thevolatile foaming agent can be exemplified by aliphatic hydrocarbons andalicyclic hydrocarbons such as propane, butane, pentane, hexane,cyclobutane, and cyclopentane, and by halogenated hydrocarbons such asmonochlorodifluoromethane, trichlorofluoromethane,dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride,ethyl chloride, and methylene chloride. The decomposable foaming agentcan be exemplified by azodicarbonamide,dinitrosopentamethylenetetramine, azobisisobutyronitrile,p,p′-oxybisbenzenesulfonyl hydrazide, citric acid, and sodiumbicarbonate.

While the amount of addition of the foaming agent to thepolypropylene-based resin composition will vary as a function of thetype of foaming agent, the equipment, the operating conditions, theexpansion ratio for the product, and so forth, the addition of 1 to 10weight parts per 100 weight parts of the polypropylene-based resincomposition is preferred in order to obtain a foam sheet having anexpansion ratio of 2 to 8 times (foam density of 0.11 to 0.46 g/cm³). Amaterial adapted for foaming must be a material that can yield asuitable expansion ratio at a suitable amount of gas.

The values of the open cell percentage and the closed cell percentageare an index for representing the state of the foam. In particular, theopen cell percentage is not more than 30% and preferably not more than15% when the foam sheet is subjected to secondary processing. At above30%, cell expansion during secondary heating exercises a substantialinfluence on the surface and readily influences container appearance.

Moreover, in order to provide a smooth appearance and provide secondarymoldability, e.g., container molding, a nonfoam layer comprising athermoplastic resin composition may be co-extruded with thepolypropylene-based resin foam sheet. A known method may be used as theco-extrusion method, and examples in this regard are multimanifoldprocedures in which lamination is performed within the die, and feedblock procedures (combining adapter procedures) in which lamination isperformed immediately before inflow into the die.

The thermoplastic resin composition constituting the nonfoam layer canbe exemplified by high-density polyethylene, low-density polyethylene,linear low-density polyethylene, homopolypropylene, random copolymers ofpropylene with ethylene or α-olefin having 4 or more carbons, blockcopolymers of propylene with ethylene or α-olefin having 4 or morecarbons, ethylene-propylene rubber, and ethylene-propylene-diene rubber.However, viewed in terms of the affinity with the foam layer and theco-extrusion characteristics, high-density polyethylene, low-densitypolyethylene, linear low-density polyethylene, homopolypropylene,propylene-ethylene block copolymers, propylene-ethylene randomcopolymers, and mixtures of the preceding are preferred. Viewed in termsof restraining heat generation during extrusion, homopolypropylene,propylene-ethylene block copolymers, propylene-ethylene randomcopolymers, and their mixtures are more preferred.

The auxiliary additive components commonly used in polyolefins, e.g.,antioxidants, neutralizing agents, heat stabilizers, light stabilizers,ultraviolet absorbers, anti-fogging agents, slip agents, antiblockingagents, antiseptics, colorants, flame retardants, and so forth, can asnecessary be incorporated into the nonfoam layer. An inorganic ororganic filler may also be added, wherein the inorganic filler can beexemplified by talc, calcium carbonate, silica, diatomaceous earth,alumina, titanium oxide, magnesium oxide, aluminum hydroxide, magnesiumhydroxide, calcium silicate, glass beads, bentonite, glass flake, glassfiber, carbon fiber, aluminum powder, molybdenum sulfide, boron fiber,potassium titanate, calcium titanate, hydrotalcite, carbon fiber, pumicepowder, mica, calcium phosphate, and aluminum phosphate, and the organicfiller can be exemplified by polymethyl methacrylate resin beads,cellulosic fiber, polyamide fiber, aramid fiber, polyester fiber, ricehusks, wood powder, tofu lees, tapioca powder, rice flour, and kenaffiber.

The polypropylene-based resin foam molding constituted as describedabove can be obtained in the form of a polypropylene-based resin foamsheet by attaching a slit die or circular die to the extruder itself forextruding the foaming agent-containing polypropylene-based resincomposition and carrying out extrusion from the slit die (T-die or coathanger type) or circular die.

The expansion ratio of the foam sheet is preferably approximately 1.5 to30 times. The thickness of the foam sheet is not particularly limited,but is preferably approximately 0.3 mm to 10 mm and more preferably is0.5 mm to 5 mm.

The average cell diameter of the foam sheet is preferably not more than300 μm, more preferably not more than 200 μm, and even more preferablynot more than 100 μm. When this average cell diameter is larger than 300μm, appearance defects, e.g., perforations and so forth, are produced inthe polypropylene-based foam sheet or the thermoformed article providedby thermoforming this sheet, and hence this is disfavored. The open cellpercentage is preferably not more than 30%, more preferably not morethan 20%, and even more preferably not more than 15%.

Diverse variations of the nonfoam layer may be provided as the nonfoamlayer used in addition to the foam layer, for example, 1) nonfoam layershaving different formulations, e.g., different pigments and so forth,may be laminated on the top and back sides; 2) the nonfoam layer may bedivided into a plurality of layers in order to provide a barrier layerand an adhesive layer; and 3) the foam layer may be divided into twolayers and another layer may be provided as a central layer.

The thickness of the multilayer foam sheet is not particularly limited,but approximately 0.3 mm to 10 mm is preferred and 0.5 mm to 5 mm ismore preferred.

The single-layer or multilayer foam sheet extruded from the die is thencooled and solidified by a known method, for example, using a polishingroll, air knife, or mandrel, and is subsequently taken up to a take-updevice or cut to prescribed dimensions using a cutter. Thepost-processing that follows cooling and solidification is notparticularly limited, and the following, for example, can be used: atreatment process that provides polar groups, e.g., a corona treatment,flame treatment, plasma treatment, and so forth; a coating step, e.g.,applying an anti-fogging agent or an antistatic agent, using a coaterroll; as well as, for example, attaching a film, printing, painting, andso forth.

In particular, film attachment can be carried out by a method that usesa pre-thermoforming lamination technique in which attachment isperformed prior to secondary molding or that uses a thermal laminationtechnique in which attachment is performed during cooling during foamlaminated sheet molding, wherein the foam laminated sheet is subjectedto an interim cooling followed by reheating with, for example, a hotroll, to effect attachment; however, attachment may be carried out byany known method.

The type of attached film is also not particularly limited and can beexemplified by films provided by the lamination of cast polypropylene(CPP) film and printed films therefrom, ethylene-vinyl alcohol copolymer(EVOH) films, and so forth, but the use is preferred of a film thatreadily adheres with polyolefin and has a polyolefin-based resindisposed on the attachment side, or a film coated with, e.g., an ink oradhesive, in which a chlorinated polypropylene or low molecular weightpolyolefin is mixed.

The foam sheet of the present invention is very well adapted tosecondary molding into moldings such as containers. The moldingtechnique used in the secondary molding can be, for example, a vacuumpressure molding technique, a vacuum molding technique, a plug moldingtechnique, a press molding technique, dual-side vacuum molding, and soforth, according to any known general method.

In the present invention, molding by a blow molding technique can becarried out on the resin that, either by itself or in a laminatedconfiguration, has been extruded to give a parison. There are noparticular limitations on the method for executing this blow molding,but a method is generally used in which a hollow molded article of thepolypropylene-based resin foam is obtained using, for example, a directblow molder or an accumulation-type blow molder.

The molded articles obtained by such molding methods can be used in awide range of fields, e.g., for stationery files, food containers,beverage cups, display cases, auto parts, commercial and industrialcomponents, and trays.

EXAMPLES

The present invention is specifically described herebelow by examples,but the present invention is not limited to or by these examples.

The properties of the polypropylene-based (multilayer) foam sheet andits constituent components were measured and assessed in the examplesand comparative examples according to assessment methods describedbelow. The resins used are also described below.

1. Property Assessments

-   (1) MFR (unit: g/10 minutes):

This was measured according to the appendix in JIS-K 6921-2. Themeasurement was performed under the following conditions: temperature of230° C. and load of 21.18 N.

-   (2) Methods for measuring the intrinsic viscosity, molecular weight    distribution, content, and α-olefin content for components (A1),    (B1), and (B2): these measurements were carried out by the    previously described methods.-   (3) Method for measuring the strain hardening exponent λmax (10)

This was derived by the previously described method using theinstrumentation and conditions indicated below.

-   (a) instrumentation: “Ares” from Rheometrics, Inc.-   (b) fixture: “Extensional Viscosity Fixture” from TA Instruments-   (c) test temperature: 180° C.-   (d) strain rate: 10/sec-   (e) sample test piece: 15 mm×10 mm press-molded sheet with a    thickness of 0.5 mm

2. Materials Used (Material A-1)

1. Preparation of the Solid Catalyst Component (c)

20 L of dried and deoxygenated n-heptane was introduced into a 50-Lstirrer-equipped tank that had been thoroughly substituted withnitrogen. This was followed by the introduction of 10 mol MgCl₂ and 20mol Ti(O-n-C₄H₉)₄ and reaction for 2 hours at 95° C. After thecompletion of the reaction, the temperature was dropped to 40° C. and 12L of methylhydropolysiloxane (20 cSt) was then introduced and a reactionwas run for 3 hours. The produced solid component was washed withn-heptane.

Then, using the aforementioned stirrer-equipped tank, 5 L of n-heptanethat had been purified as described above was introduced into this tankand 3 mol, as the Mg atom, of the solid component synthesized asdescribed above was introduced. Then, 5 mol SiCl₄ in 2.5 L n-heptane wasmixed and this was introduced into the tank over 30 minutes at 30° C.and a reaction was carried out for 3 hours at 70° C. Washing withn-heptane was performed after the completion of the reaction.

2.5 L n-heptane was then introduced into the aforementionedstirrer-equipped tank; 0.3 mol phthaloyl chloride was mixed;introduction was carried out over 30 minutes at 70° C.; and a reactionwas run for 1 hour at 90° C. Washing with n-heptane was performed afterthe completion of the reaction. Then, 2 L TiCl₄ was introduced and areaction was run for 3 hours at 110° C. After the completion of thereaction, washing with n-heptane yielded a solid component (c1) forproducing the solid catalyst component (c). The titanium content in thissolid component was 2.0 weight %.

Then, 8 L n-heptane and 400 g of the solid component (c1) synthesized asdescribed above were introduced into the aforementioned stirrer-equippedtank that had been substituted with nitrogen; 0.6 L SiCl₄ was introducedas a component (c2); and a reaction was run for 2 hours at 90° C. Afterthe completion of the reaction, 0.54 mol (CH₂═CH)Si(CH₃)₃ as a component(c3), 0.27 mol (t-C₄H₉)(CH₃)Si(OCH₃)₂ as a component (c4), and 1.5 molAl(C₂H₅)₃ as a component (c5) were additionally introduced in theindicated sequence and contact was performed for 2 hours at 30° C. Afterthe completion of this contact, thorough washing with n-heptane wascarried out to obtain 390 g of a component (c) that was mainly magnesiumchloride. Its titanium content was 1.8 weight %.

2. Production of Propylene-Based Block Copolymer

A 400-L stirrer-equipped stainless steel autoclave was thoroughlysubstituted with propylene gas and 120 L of a dried and deoxygenatedn-heptane was introduced as the polymerization solvent. 30 gtriethylaluminum, 12 L hydrogen, and 10 g of the aforementioned catalystcomponent (c) were then introduced at a temperature of 70° C. Afterraising the autoclave to an internal temperature of 75° C., propylenewas supplied at 20.7 kg/hr and hydrogen was supplied at 20.6 L/hr. Thesupply of propylene and hydrogen was stopped after 200 minutes. Duringthe interval of propylene and hydrogen supply, the pressure within thevessel gradually rose and ultimately rose to 0.46 MPaG. After this, aresidual polymerization was carried out, and, at the time point at whichthe pressure in the vessel reached 0.35 MPaG, the gas within thereaction vessel was purged to 0.03 MPaG to obtain a propylene polymer(first stage polymerization step).

Then, the autoclave was set at an internal temperature of 65° C.,followed by the introduction of 16.0 cc n-butanol and then the supply ofpropylene at 2.4 kg/hr and ethylene at 1.6 kg/hr. After 90 minutes, thesupply of ethylene and propylene was stopped to finish thepolymerization. The pressure was 0.03 MPaG at the start of ethylene andpropylene supply and was 0.09 MPaG when supply was stopped (second stagepolymerization step).

The obtained slurry was transferred to a following stirrer-equippedtank; 2.5 L butanol was added and treatment was carried out for 3 hoursat 70° C.; transfer was then carried out to a following stirrer-equippedtank, 100 L pure water in which 20 g sodium hydroxide was dissolved wasadded, and a treatment was performed for 1 hour; and this was followedby separation of the water layer after quiescence to remove the catalystresidue. The slurry was processed with a centrifugal separator to removethe heptane and the heptane was then completely eliminated by treatingfor 3 hours in a drier at 80° C. to obtain 59.7 kg of a sample.

The obtained material was a polypropylene-based resin composition asfollows: the propylene-α-olefin copolymer portion was 6.6 weight % ofthe total mass, contained 44.7 weight % ethylene as the α-olefin, had anintrinsic viscosity η of 14.8 dL/g, and had a ratio between theweight-average molecular weight and the number-average molecular weight(Mw/Mn) of 13.3; the propylene homopolymer portion was 93.4 weight % ofthe total mass; and the polypropylene-based resin composition had an MFR(230° C., load of 2.16 kg) of 12 g/10 minutes, exhibited strainhardening (“yes” for strain hardening) in an extensional viscositymeasurement at 180° C., and had a degree of strain hardening (λmax (10))of 2.0.

(Materials A-2 to A-7 and A-9 to A-11)

Materials with the compositions and properties given in Table 1 wereobtained by the same method as for material A-1 by adjusting the amountof hydrogen and ethylene.

(Material A-8)

Homopolypropylene (product of Japan Polypropylene Corporation, productname “Novatec (registered trademark) PP MA 3”, MFR (230° C., 2.16 kgload): 10 g/10 minutes) was used.

The properties of materials A-1 to A-11 are given in the following Table1.

TABLE 1 material material material material material material materialmaterial material material material A-1 A-2 A-3 A-4 A-5 A-6 A-7 A-8 A-9A-10 A-11 component content 6.6 8.1 13.1 14.7 13.9 10.1 23.0  0.0 10.010.0 10.0 (A1) α-olefin 44.7 46.3 81.3 46.1 78.9 88.8 64.2 — 32.0 16.620.2 content intrinsic 14.8 9.9 7.5 3.8 9.8 10.1 7.2 — 9.7 8.7 10.0viscosity η Mw/Mn 13.3 6.3 8.4 4.7 7.3 18.4 5.1 — 5.8 6.2 6.7 componentcontent 93.4 91.9 86.9 85.3 86.1 89.9 77.0 100.0 90.0 90.0 90.0 (A2)total mass MFR 12.0 9.0 8.0 10.0 1.5 2.7 1.2  10.0 6.2 5.2 5.8 strainyes yes yes no yes yes yes no yes yes yes hardening λmax (10) 2.0 2.41.2 — 1.3 2.2 1.9 — 2.4 3.3 2.9

(Material B-1)

70 L n-heptane, 3 g Mg-supported titanium catalyst (solid catalystprepared proceeding as in Example 1 of Japanese Patent ApplicationLaid-open No. H4-348113), and 10 g triethylaluminum were added to a200-L stainless steel autoclave; the temperature was raised to 70° C.;and hydrogen and propylene were supplied to produce a propylenehomopolymer with MFR=50 g/10 minutes in an amount corresponding to 70weight % of the total polymer. A resin composition was then prepared bypurging the hydrogen and supplying ethylene and propylene to produce, inan amount corresponding to 30 weight % of the total polymer, an ethylene• propylene copolymer having an ethylene content of 10 weight % and aweight-average molecular weight of 4,800,000.

(Materials B-2 to B-9)

Resin compositions with various indices were obtained by the same methodas for material B-1, but changing the polymerization conditions for thepropylene homopolymer (first stage polymerization step) and the ethylene• propylene copolymer (second stage polymerization step).

The properties of these materials B-1 to B-9 are given in the followingTable 2.

TABLE 2 material material material material material material materialmaterial material B-1 B-2 B-3 B-4 B-5 B-6 B-7 B-8 B-9 component content70 80 70 80 80 40 91 70 80 (B1) MFR 50 40 100 40 40 50 10 20 200comonomer 0 0 0 0 0 0 0 0 0 content component content 30 20 30 20 20 609 30 20 (B2) comonomer 10 10 6 0 80 10 10 10 10 content Mw (10⁴) 480 36054 360 360 180 180 45 180 total mass MFR 1 5 4 5 5 0.3 5 8 28 MT 37 3017 100 2 90 2 2 1 0.97*log 1.23 1.91 1.81 1.91 1.91 0.72 1.91 2.11 2.63MFR + 1.23 τD 800 380 150 1800 80 1200 60 50 40

For the individual materials A and materials B described above, pelletsof each component were obtained by adding the following as additives to100 weight parts of the particular propylene-based resin composition andmelt mixing in a twin-screw extruder at 200° C.: 0.1 weight partstetrakis[methylene-3-(3′,5′-di-t-butyl-4′-hydroxyphenyl) propionate]methane (trade name: “IRGANOX 1010”, from Ciba Specialty ChemicalsCorporation) as a phenolic antioxidant, 0.1 weight partstris(2,4-di-t-butylphenyl) phosphite (trade name: “IRGAFOS 168”, fromCiba Specialty Chemicals Corporation) as a phosphite-type antioxidant,and 0.1 weight parts calcium stearate (trade name: “Calcium Stearate”,from the NOF Corporation) as a neutralizing agent.

Examples 1-1 to 1-3 and 1-7 to 1-9 and Comparative Examples 1-1 to 1-5

Evaluation of Foam Extrusion Using a Slit Die

Using the pellets of the particular components described in Table 3,mixing by dry blending was carried out with 0.5 weight parts of afoaming agent (sodium bicarbonate/citric acid-type chemical foamingagent, trade name: “CF40E”, from Clariant) as a foam nucleating agent.Extrusion was performed at an extrusion rate of approximately 60 kg/hourusing a 65 cpmm extruder (from PLA GIKEN Co., Ltd., screw tiptemperature=180° C.). Melting, mixing, and plasticization were firstperformed in the first half of the extruder; then, in the middle regionof the extruder, carbon dioxide gas was injected at 0.23 kg per hourfrom a carbon dioxide gas quantitative feed apparatus (from Showa TansanCo., Ltd.); in the remaining region of the extruder, the carbon dioxidegas was mixed into the plasticized resin to produce a foamingagent-containing resin in which carbon dioxide gas was uniformlydispersed; casting onto a polishing roll from a 750 mm-wide T-die (settemperature=180° C.) was subsequently carried out; and a foam sheetsample was then obtained by cooling, solidification, and take up.

The expansion ratio, open cell percentage, closed cell percentage, andcell morphology were then observed using this sheet. Since the amount ofcarbon dioxide gas added is an amount of gas sufficient to obtain arange having 2.5 times as the minimum, at below this range the materialcan be rated as a material that is resistant to inflation, i.e., as amaterial not suitable for foaming.

-   -   Open cell percentage (unit: %) and closed cell percentage (unit:        %):

The air specific gravity was measured using an air pycnometer (Model 930from Toshiba-Beckman Co., Ltd.) as the measurement instrument, and theopen cell percentage and closed cell percentage were measured using thefollowing formulas and excluding the deposition of any nonfoam layer dueto multilayering.open cell percentage=(apparent foam layer volume−measurementvalue)×100/apparent foam layer volumeclosed cell percentage=(measurement value−foam layerweight/0.9)/apparent foam layer volume×100

Evaluation in Thermoforming

Using the sheet obtained as described above, round containers of length22 cm, width 22 cm, and depth 5 cm were fabricated using a vacuumpressure molder from Asano Laboratories Co., Ltd., and an upper andlower heater temperature of 380° C., and the container moldability andappearance were visually evaluated.

The following scales were used for the evaluations.

Container Moldability:

-   ◯: Molding could be performed without problems such as sagging    during molding and film rupture during heating.-   Δ: Some sagging occurred, but film rupture during heating did not    occur and molding could be performed.-   ×: There was substantial sagging and/or film rupture during heating    occurred, and molding could not be performed.

Container Appearance:

-   ◯: Unevenness in container appearance, bridging, and so forth, were    not produced and maintenance of the wall thickness was also    favorable and an excellent container was obtained.-   Δ: Some bridging and so forth, was produced, as was some unevenness    in container appearance, and maintenance of the wall thickness was    somewhat unsatisfactory, but a useable container was obtained.-   ×: A container was obtained in which bridging and so forth, was    produced, there was severe unevenness in container appearance, and    maintenance of the wall thickness was unsatisfactory.

These results are shown in Table 3 below.

TABLE 3 examples comparative examples 1-1 1-2 1-3 1-7 1-8 1-9 1-1 1-21-3 1-4 1-5 component (A) A-1 A-2 A-3 A-9 A-10 A-ll A-4 A-5 A-6 A-7 A-8component content 6.6 8.1 13.1 10.0 10.0 10.0 14.7 13.9 10.1 23.0 0.0(A1) α-olefin 44.7 46.3 81.3 32.0 16.6 20.2 46.1 78.9 88.8 64.2 —content intrinsic 14.8 9.9 7.5 9.7 8.7 10.0 3.8 9.8 10.1 7.2 — viscosityη Mw/Mn 13.3 6.3 8.4 5.8 6.2 6.7 4.7 7.3 18.4 5.1 — component content93.4 91.9 86.9 90.0 90.0 90.0 85.3 86.1 89.9 77.0 100.0 (A2) total massMFR 12.0 9.0 8.0 6.2 5.2 5.8 10.0 1.5 2.7 1.2 10.0 λmax (10) 2.0 2.4 1.22.4 3.3 2.9 none 1.3 2.2 1.9 none thickness, mm 1.5 1.5 1.5 1.5 1.5 1.51.0 1.4 1.5 1.6 1.0 specific gravity, 0.30 0.25 0.30 0.32 0.32 0.31 0.280.43 0.37 0.32 0.49 g/cc expansion ratio, 3.0 3.5 3.0 2.8 2.9 2.9 3.02.1 2.4 2.8 1.9 times open cell 15 17 28 16 12 10 52 76 70 74 89percentage, vol % closed cell 85 83 72 84 88 90 48 24 30 26 11percentage, vol % container ∘ ∘ ∘ ∘ ∘ ∘ x ∘ ∘ ∘ x moldability container∘ ∘ ∘ ∘ ∘ ∘ x x x x x appearance

Examples 1-4 to 1-6 and Comparative Examples 1-6 to 1-9

Evaluation of Foam Extrusion Using a Blow Molder:

Using the pellets of the components indicated in Table 4, mixing by dryblending was carried out with 3 weight parts of the aforementioned“CF40E” foaming agent (sodium bicarbonate, citric acid-type chemicalfoaming agent) as a foam nucleating agent, followed by supply to adirect blow molder with a die temperature set to 170° C. to obtain afoamed parison.

Appearance of the Surface of the Molded Article:

The surface smoothness of the obtained foamed parison was evaluatedusing the following 3 levels.

-   ◯: smooth when the surface is manually rubbed-   Δ: coarse when the surface is manually rubbed-   ×: unevenness is felt when the surface is manually rubbed

In this case, ◯ and Δ are levels judged to be practically useful.

Expansion Ratio:

The ratio between the specific gravity of the polypropylene-based resincomposition used as the starting material and the specific gravity ofthe obtained foamed parison was used as the expansion ratio. Thespecific gravity was determined by the water displacement method.

An expansion ratio of 1.8 times and greater is considered to beexcellent.

The results of these evaluations are given in Table 4.

TABLE 4 examples comparative examples 1-4 1-5 1-6 1-6 1-7 1-8 1-9component (A) A-1 A-2 A-3 A-4 A-5 A-6 A-7 component content 6.6 8.1 13.114.7 13.9 10.1 23.0 (A1) α-olefin 44.7 46.3 81.3 46.1 78.9 88.8 64.2content intrinsic 14.8 9.9 1.5 3.8 9.8 10.1 7.2 visco- sity η Mw/Mn 13.36.3 8.4 4.7 7.3 18.4 5.1 component content 93.4 91.9 86.9 85.3 86.1 89.977.0 (A2) total mass MFR 12.0 9.0 8.0 10.0 1.5 2.7 1.2 λmax 2.0 2.4 1.2none 1.3 2.2 1.9 (10) thickness, mm 3.0 3.2 2.8 2.2 2.1 2.0 1.7 specificgravity, g/cc 0.45 0.43 0.47 0.60 0.64 0.69 0.75 expansion ratio, times2.0 2.1 1.9 1.5 1.4 1.3 1.2 appearance of the ∘ ∘ ∘ x Δ Δ ∘ moldedarticle

Examples 2-1 to 2-7, 12 to 14, and Comparative Examples 2-1 to 2-12

Evaluation of Foam Extrusion Using a Slit Die

Using the pellets of the particular components described in Tables 3 to5, mixing by dry blending was carried out with 0.5 weight parts of afoaming agent (sodium bicarbonate/citric acid-type chemical foamingagent, trade name: “CF40E”, from Clariant) as a foam nucleating agent.Extrusion was performed at an extrusion rate of approximately 60 kg/hourusing a 65 calm extruder (from PLA GIKEN Co., Ltd., screw tiptemperature=180° C.). Melting, mixing, and plasticization were firstperformed in the first half of the extruder; then, in the middle regionof the extruder, carbon dioxide gas was injected at 0.23 kg per hourfrom a carbon dioxide gas quantitative feed apparatus (from Showa TansanCo., Ltd.); in the remaining region of the extruder, the carbon dioxidegas was mixed into the plasticized resin to produce a foamingagent-containing resin in which carbon dioxide gas was uniformlydispersed; casting onto a polishing roll from a 750 mm-wide T-die (settemperature=180° C.) was subsequently carried out; and a foam sheetsample was then obtained by cooling, solidification, and take up.

The expansion ratio, open cell percentage, closed cell percentage, andcell morphology were then observed using this sheet. Since the amount ofcarbon dioxide gas added is an amount of gas sufficient to obtain arange having 2.5 times as the minimum, at below this range the materialcan be rated as a material that is resistant to inflation, i.e., as amaterial not suitable for foaming.

Open cell percentage (unit: %) and closed cell percentage (unit: %):

The air specific gravity was measured using an air pycnometer (Model 930from Toshiba-Beckman Co., Ltd.) as the measurement instrument, and theopen cell percentage and closed cell percentage were measured using thefollowing formulas and excluding the deposition of any nonfoam layer dueto multilayering.open cell percentage=(apparent foam layer volume−measurementvalue)×100/apparent foam layer volumeclosed cell percentage=(measurement value−foam layerweight/0.9)/apparent foam layer volume×100

Evaluation in Thermoforming

Using the sheet obtained as described above, round containers of length22 cm, width 22 cm, and depth 5 cm were fabricated using a vacuumpressure molder from Asano Laboratories Co., Ltd., and an upper andlower heater temperature of 380° C., and the container moldability andappearance were visually evaluated.

The following scales were used for the evaluations.

Container Moldability:

-   ◯: Molding could be performed without problems such as sagging    during molding and film rupture during heating.-   Δ: Some sagging occurred, but film rupture during heating did not    occur and molding could be performed.-   ×: There was substantial sagging and/or film rupture during heating    occurred, and molding could not be performed.

Container Appearance:

-   ◯: Unevenness in container appearance, bridging, and so forth, were    not produced and maintenance of the wall thickness was also    favorable and an excellent container was obtained.-   Δ: Some bridging and so forth, was produced, as was some unevenness    in container appearance, and maintenance of the wall thickness was    somewhat unsatisfactory, but a useable container was obtained.-   ×: A container was obtained in which bridging and so forth, was    produced, there was severe unevenness in container appearance, and    maintenance of the wall thickness was unsatisfactory.

These results are shown in Tables 5 to 7 below.

TABLE 5 Example Example Example Example Comparative Example Example 2-12-2 2-3 2-4 Example 2-1 2-5 2-13 component (A) A-1 A-1 A-1 A-1 A-1 A-1A-1 amount of 80 80 80 70 65 95 98 addition component (B) B-1 B-2 B-3B-3 B-3 B-3 B-3 amount of 20 20 20 30 35 5 2 addition thickness, mm 1.41.3 1.5 1.5 1.3 1.5 1.5 specific gravity, 0.28 0.28 0.32 0.29 0.38 0.320.31 g/cc expansion ratio, 3.2 3.2 2.8 3.1 2.4 2.8 2.9 times open cell 97 14 19 31 13 16 percentage, vol % closed cell 91 93 86 81 69 87 84percentage, vol % container ∘ ∘ ∘ ∘ ∘ ∘ ∘ moldability container ∘ ∘ ∘ Δx ∘ ∘ appearance

TABLE 6 Example Example Example Comparative Comparative ComparativeComparative Comparative Example 2-1 2-6 2-7 Example 2-2 Example 2-3Example 2-4 Example 2-5 Example 2-6 2-12 component (A) A-1 A-2 A-3 A-4A-5 A-6 A-7 A-8 A-11 amount of 80 80 80 80 80 80 80 80 80 additioncomponent (B) B-1 B-1 B-1 B-1 B-1 B-1 B-1 B-1 B-3 amount of 20 20 20 2020 20 20 20 20 addition thickness, mm 1.4 1.3 1.5 1.5 1.5 1.5 1.5 1.51.5 specific gravity, 0.28 0.31 0.30 0.29 0.43 0.32 0.36 0.45 0.31 g/ccexpansion ratio, 3.2 2.9 3.0 3.1 2.1 2.8 2.5 2.0 2.9 times open cell 9 822 48 38 31 34 35 12 percentage, vol % closed cell 91 92 78 52 62 69 6465 88 percentage, vol % container ∘ ∘ ∘ x x x x x ∘ moldabilitycontainer ∘ ∘ ∘ Δ x x x x ∘ appearance

TABLE 7 Example Example Example Comparative Comparative ComparativeComparative Comparative Comparative 2-1 2-2 2-3 Example 2-7 Example 2-8Example 2-9 Example 2-10 Example 2-11 Example 2-12 component (A) A-1 A-1A-1 A-1 A-1 A-1 A-1 A-1 A-1 amount of 80 80 80 80 80 80 80 81 82addition component (B) B-1 B-2 B-3 B-4 B-5 B-6 B-7 B-8 B-9 amount of 2020 20 30 35 5 2 3 4 addition thickness, mm 1.4 1.3 1.5 1.0 1.0 0.8 1.01.4 1.2 specific gravity, 0.28 0.28 0.32 0.38 0.36 0.50 0.39 0.33 0.43g/cc expansion ratio, 3.2 3.2 2.8 2.4 2.5 1.8 2.3 2.7 2.1 times opencell 9 7 14 43 36 24 32 32 31 percentage, vol % closed cell 91 93 86 5764 76 68 68 69 percentage, vol % container ∘ ∘ ∘ Δ Δ Δ Δ x x moldabilitycontainer ∘ ∘ ∘ x x x x Δ x appearance

Examples 2-8 to 2-11, 2-14, and 2-15 and Comparative Example 2-13

5. Evaluation of Foam Extrusion Using a Blow Molder:

Using the pellets of the components indicated in Table 8, and after dryblending at the ratios shown in Table 6, mixing by dry blending wascarried out with 3 weight parts of the aforementioned “CF40E” foamingagent (sodium bicarbonate, citric acid-type chemical foaming agent) as afoam nucleating agent, followed by supply to a direct blow molder with adie temperature set to 170° C. to obtain a foamed parison.

Appearance of the Surface of the Molded Article:

The surface smoothness of the obtained foamed parison was evaluatedusing the following 3 levels.

-   ◯: smooth when the surface is manually rubbed-   Δ: coarse when the surface is manually rubbed-   ×: unevenness is felt when the surface is manually rubbed

In this case, ◯ and Δ are levels judged to be practically useful.

Expansion Ratio:

The ratio between the specific gravity of the polypropylene-based resincomposition used as the starting material and the specific gravity ofthe obtained foamed parison was used as the expansion ratio. Thespecific gravity was determined by the water displacement method.

An expansion ratio of 1.8 times and greater is considered to beexcellent.

Resistance to Drawdown:

In the extrusion for a length of 1.0 m of a foamed parison at a dietemperature set to 170° C., a ratio of the wall thickness at the upperpart of the parison to the wall thickness at the lower part of theparison of 0.8 to 1.0 was rated as excellent or ◯, while a ratio lessthan 0.8, or when molding was defective or not possible, was rated aspoor or ×.

The results of these evaluations are given in Table 8.

TABLE 8 Example Example Example Example Comparative Example Example 2-82-9 2-10 2-11 Example 2-13 2-15 2-14 component (A) A-1 A-1 A-1 A-1 A-1A-1 A-1 amount of 80 80 80 70 65 95 98 addition component (B) B-1 B-2B-3 B-3 B-3 B-3 B-3 amount of 20 20 20 30 35 5 2 addition thickness, mm3.5 3.5 3.4 3.4 3.4 3.1 3.1 specific gravity, 0.39 0.40 0.40 0.38 0.470.41 0.41 g/cc expansion ratio, 2.3 2.3 2.3 2.4 1.9 2.2 2.2 timesappearance of ∘ ∘ ∘ Δ x ∘ ∘ the molded article resistance to ∘ ∘ ∘ ∘ ∘ ∘x drawdown

INDUSTRIAL APPLICABILITY

The polypropylene-based resin composition of the presentinvention—because it can provide a foam molding that exhibits anexcellent closed cell characteristic and excellent extrusioncharacteristics, that is light weight and has a rigid feel, and that hasan excellent recyclability—can be very favorably used for, for example,stationery files, food containers, beverage cups, display cases, autoparts, commercial and industrial components, and trays, and thus has avery high industrial and commercial value.

The invention claimed is:
 1. A polypropylene-based resin composition,comprising component (A) and component (B), wherein, based on 100 weight% sum of components (A) and (B), a component (A) content is less than100 weight % but at least 70 weight % and a component (B) content isgreater than 0 weight % but not more than 30 weight %, wherein component(A) is a propylene-based resin composition that comprises apropylene-α-olefin copolymer (component (A1)) and a propylenehomopolymer (component (A2)), components (A1) and (A2) are obtained bypolymerization by a multistage polymerization method, thepropylene-based resin composition has a component (A1) content of 1 to20 weight % and a component (A2) content of 99 to 80 weight %, based ona sum of components (A1) and (A2) of 100 weight %, and has a melt flowrate in the range from 5 to 20 g/10 minutes and exhibits strainhardening in a measurement of extensional viscosity at a temperature of180° C. and a strain rate of 10 s⁻¹, the propylene-α-olefin copolymer(A1) satisfies conditions (A-1) to (A-3): (A-1) an α-olefin content of15 to 85 weight %, where a total amount of monomer constitutingcomponent (A1) is 100 weight %; (A-2) an intrinsic viscosity η of 5 to20 dL/g; and (A-3) a Mw/Mn of 5 to 15, component (B) is apropylene-based resin composition comprising a propylene homopolymer ora propylene-α-olefin copolymer having a content of non-propyleneα-olefin of less than 1 weight % (component (B1)), which has an MFR of10 to 1000 g/10 minutes, and a propylene-α-olefin copolymer (component(B2) that has a weight-average molecular weight of 500,000 to 10,000,000and a content of non-propylene α-olefin of 1 to 15 weight %, components(B1) and (B2) are obtained by polymerization by a multistagepolymerization method, and the propylene-based resin composition has acomponent (B1) content of 50 to 90 weight % and a component (B2) contentof 50 to 10 weight %, where a sum of components (B1) and (B2) is 100weight %, and satisfies conditions (B-1) to (B-3): (B-1) an MFR of 0.1to 20 g/10 minutes; (B-2) a relationship between a melt tension (MT) andthe MFR satisfying the following formulalog MT>−0.97×log MFR+1.23; and (B-3) a longest relaxation time (τd) ofat least 100 seconds.
 2. The composition according to claim 1, whereinthe component (A) content is from 70 to 97 weight % and the component(B) content is from 3 to 30 weight %.
 3. The composition according toclaim 1, wherein component (A) has a strain hardening exponent λmax (10)of at least 1.2 in the measurement of extensional viscosity at atemperature of 180° C. and a strain rate of 10 s⁻¹.
 4. The compositionaccording to claim 1, wherein the α-olefin of the propylene-α-olefincopolymer (A1) is selected from the group consisting of ethylene,butene, pentene, hexene, heptene, nonene, decene, 1-methylbutene, and1-methylpentene.
 5. The composition according to claim 1, wherein theintrinsic viscosity η of the propylene-α-olefin copolymer (A1) is from6.5 to 17 dL/g.
 6. The composition according to claim 1, wherein theintrinsic viscosity η of the propylene-α-olefin copolymer (A1) is from 8to 15 dL/g.
 7. The composition according to claim 1, wherein the Mw/Mnof the propylene-α-olefin copolymer (A1) is from 10 to
 15. 8. Thecomposition according to claim 1, wherein the propylene homopolymer (A2)has a stereoregularity of at least 96%.
 9. A polypropylene-based resinfoam molding, wherein the molding is molded by a process comprising:adding a foaming agent to the polypropylene-based resin compositionaccording to claim 1; and carrying out extrusion foam molding thereof.10. The molding according to claim 9, wherein the molding is a foamsheet molded by extrusion from a slit die or circular die.
 11. Apolypropylene-based resin foam thermoformed article formed by a processcomprising thermoforming the foam sheet according to claim
 10. 12. Apolypropylene-based resin foam hollow molding, wherein the molding is ahollow molding molded by a process comprising: adding a foaming agent tothe polypropylene-based resin composition according to claim 1;extruding the composition to obtain a parison; and subsequentlyperforming blow molding within a mold.